The invention relates to a lighting device for the uniform illumination of curved, uneven, or polyhedral surfaces, comprising a plurality of flat chip-on-board LED modules, which are arranged adjacent to each other at least in pairs, wherein each chip-on-board LED module has a plurality of light-emitting LEDs. The invention further relates to an lighting unit and a use.
One field of application that requires a uniform illumination of curved, polyhedral, or uneven surfaces is the curing and light exposure needed for drying, hardening, or exposure of lacquers, adhesives, resins, and other light-reactive materials, with which the insides or outsides of uneven bodies are coated.
One example here is duct relining, where it is known to provide the inside of pipes with a light-curable coating or substance in the form of a hose. For curing a so-called “pipe liner,” a resin-saturated glass-fiber fabric having protective plastic films on the outer surfaces, a lamp is forced through the hose or through the pipe for the duct relining, in order to progressively dry and cure the coating material section by section by an intensive illumination. Suitable lamp systems ideally have a curved shape for bends up to 90°. Typical diameters of corresponding coated pipes and hoses are in the range of a few centimeters up to several meters.
This procedure requires a uniform exposure to light, in order to achieve a uniform drying and curing of the coating material on all sides. Typical homogeneity tolerances for the illumination lie in the range of less than +15% with respect to a defined average. For this application, the illumination intensities on an illuminated inner wall are a few μW/cm2 up to 100 W/cm2.
In order to achieve a high light power, corresponding known lamp systems are provided with a diameter that is only a few millimeters less than the inner diameter of the pipe that they are designed for. However, the lamp could also be located up to a few meters from the surface to be illuminated.
Similar requirements are known for the interior illumination of other radially symmetric, convex hollow bodies. This applies, for example, in the field of lighting equipment, e.g., for architectural lighting, for UV curing, and for the exposure to light of elongated bodies or hollow spaces having specified cross-sectional geometries. Suitable geometries are, for example, pipes, cones, spheres, polyhedral bodies, or the like.
For the application example of the light-curing duct relining, gas-discharge lamps until now have usually been used that provide an intensive light output. The traditionally used gas-discharge-based lamps develop strong heat emissions or infrared emissions that heat up the object and the coating to be cured if the lamp comes too close to the object to be illuminated or if the illumination lasts too long. For UV curing processes, this means that the polymers to be cross-linked can disassociate. In duct relining, this can result in thermal damage in the liner material to be cured.
The known lamps are suitable, above all, for larger pipe diameters, but due to their overall size are less suitable for smaller pipe diameters, for example in building connections, having typical pipe diameters corresponding to a nominal diameter of 160 mm or smaller. There are no gas-discharge lamp systems of this size available, that can be pulled through curves having angles of 45° or 90°.
For small overall sizes, the traditional UV lamp technology is limited by the achievable minimum size of the lamps. Another limitation in this respect is also due to the requirement for a mechanically robust holder and protective device for the lamps, which usually consist of a glass enveloping body filled with a substance, in which the gas discharge takes place between two opposing electrodes or by an electrode-less excitation with microwaves. With a suitably mechanically robust holder or protective device, for example in the form of metal rods surrounding the lamp, shadows in the emitted radiation must be reckoned with. These inhomogeneities in the emissions are disadvantageous, if a uniform irradiation is required, for example in UV curing.
In particular, the use of several traditional glass bulb lamps for achieving high irradiation intensities makes it more difficult to achieve a homogeneous illumination due to the significant geometric expansion of these lamps, when these are arranged one next to the other in the peripheral direction, for example of a pipe. This results from the fact that a good overflow of the emitted radiation fields takes place only at a geometric spacing corresponding to the spacing of the emission centers, so that drops in the radiation intensity due to the lack of emissions between the emission centers of the lamps lead to strong inhomogeneities in the peripheral direction. In this case, possibly expensive optics must be used for the homogenization of the illumination.